Discharging roller, method of manufacturing the same, and recording apparatus incorporating the same

ABSTRACT

In order to manufacture a discharging roller which discharges a recording medium from a recording apparatus, there are a first die formed with a first recess extending in an axial direction of a shaft portion of the discharging roller, and a second die formed with a second recess extending in the axial direction. The first die and the second die are combined such that the first recess and the second recess face to form a continuous cavity. Synthetic resin is injected into the cavity to mold a bore portion of the shaft portion.

BACKGROUND OF THE INVENTION

The present invention relates to a discharging roller which discharges arecording medium on which data recording has been performed, a method ofmanufacturing the discharging roller, and a recording apparatusincorporating the discharging roller.

An ink jet printer that Is one of recording apparatuses is generallyconstituted so as to supply a sheet stored in a sheet feeding tray to asheet feeding roller, transport the supplied sheet to a recordingsection while holding between a sheet feeding roller pair, cause arecording head to eject an ink droplet onto the sheet to performrecording, and discharge the sheet to a sheet ejection tray whileholding between a discharging roller pair. Since recording on the sheetis thus performed between the discharging roller pair and the feedingroller pair, a rotary speed of the discharging roller is set slighthigher than that of the feeding roller to tense the sheet between thedischarging roller and the feeding roller, whereby the sheet becomesflat to improve recording accuracy.

FIG. 13A is a perspective view showing a first related-art dischargingroller as disclosed in Japanese Patent Publication No. 10-129910A. Thisdischarging roller 1 is formed so that a shaft portion 2 made ofplastics becomes longer than at least recordable maximum sheet width,and plural roller portions 3 made of rubber are fitted in the shaftportion 2 with constant intervals. As shown in FIG. 13B, such thedischarging roller 1 is formed so that a circular portion of a sectionalshape of the shaft portion 2 has diameter Ds and a cross-shaped portionthereof has thickness t, and the diameter Ds must be smaller thandiameter Dr of the roller portion 3. Specifically, the diameter Ds is6.80 mm and the diameter Dr is 11.26 mm. Therefore, the proportion ofthe outer diameter of the shaft portion to the outer diameter of theroller portion is 60.4%.

FIG. 14 is a section view showing a second related-art dischargingroller as disclosed in Japanese Patent Publication No. 10-291674A. Thisdischarging roller comprises a cylindrical body 30 and shaft portions 20extended from both longitudinal ends of the cylindrical body 30 andhaving a smaller diameter than that of the cylindrical body 30. Thecylindrical body 30 and the shaft portions 20 are made of plastics. Theshaft portions respectively have a hollowed portion which are formed bya core 75 or a resin injection port 77. One of the hollowed portion Iscommunicated with a cavity 31 formed inside the cylindrical body 30.

In case that the first related-art discharging roller 1 is formed ofsynthetic resin, it is necessary to provide thickness deletion (thickremoval) so as not to make the discharging roller thick in order toprevent deformation or sink of the shaft caused by internal stress inmolding. Therefore, only rigidity of a certain level can be secured.Further, since the rotation speed of the discharging roller 1 is set soas to become higher than that of the feeding roller, power pulled ontothe feeding roller side acts on the discharging roller. Therefore, thereis anxiety that deformation such as a flexure is produced in thedischarging roller 1.

Since the deformation of the discharge roll 1 such as the flexure isrestored when a rear end of the sheet is released from the feedingroller pair, there are instances where a so-called flip phenomenon ofsheet is produced at this time. In case that an ink jet printer canrecord data on the whole surface of sheet or the nearly whole surfacethereof, recording is continued to the rear end of the sheet even afterthe rear end of the sheet is released from the feeding roller pair.Therefore, in case that the above flip phenomenon is produced, a badinfluence is exerted on recording accuracy.

Regarding the second related-art discharging roller shown in FIG. 14,the sink 34 tends to be produced when auxiliary cavities 40 are filledwith the injected resin. This causes deformation or the rigidityreduction of the discharging roller surface. Moreover, if flashes areformed on an outer circumferential surface of the shaft portions 20 andthe cylindrical body 30 at the plastic molding process performed by thegas injection method, for example, there is anxiety that the flashescause sliding load increase of a bearing portion or deterioration ofsheet feeding accuracy.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a dischargingroller which can prevent the flip phenomenon at the discharging time ofa recording medium, a method of manufacturing such a discharging roller,and a recording apparatus incorporating such a discharging roller.

In order to achieve the above object, according to the invention, thereis provided a discharging roller which discharges a recording mediumfrom a recording apparatus, comprising a hollowed shaft portioncomprised of synthetic resin.

Preferably, the synthetic resin is comprised of an additive to enhancestiffness of the shaft portion.

Preferably, the discharging roller further comprises a roller portionformed on an outer periphery of the shaft portion. Here, a proportion ofan outer diameter of the shaft portion with respect to an outer diameterof the roller portion is not less than 60.5%.

According to the invention, there is also provided a die for molding adischarging roller which discharges a recording medium from a recordingapparatus, the die comprising:

-   -   a first die, formed with a first recess extending in an axial        direction of a shaft portion of the discharging roller; and    -   a second die, formed with a second recess extending in the axial        direction, the second die combined with the first die such that        the first recess and the second recess face to form a continuous        cavity for molding a bore portion of the shaft portion.

Preferably, the first recess is formed on a bottom face of a recessedportion of the first die, and the second recess is formed on a convexportion of the second die which is fitted into the recessed portion.

Here, it is preferable that an entrance corner of the recessed portionand a corner portion opposing to the entrance corner are tapered.

Preferably, at least one of the first die and the second die is formedwith a fluid passage through which a fluid for cooling the cavity flows.

According to the invention, there is also provided a method ofmanufacturing a discharging roller which discharges a recording mediumfrom a recording apparatus, the method comprising steps of:

-   -   providing a first die, formed with a first recess extending in        an axial direction of a shaft portion of the discharging roller;    -   providing a second die, formed with a second recess extending in        the axial direction;    -   combining the first die and the second die such that the first        recess and the second recess face to form a continuous cavity;        and    -   injecting synthetic resin into the cavity to mold a bore portion        of the shaft portion.

Preferably, the manufacturing method further comprises a step ofregulating temperature of the cavity such an extent that the injectedsynthetic resin is solidified in a state where it is adhered onto aninner face of the cavity.

Preferably, the manufacturing method further comprises a step ofinjecting gas into the cavity to form a void in the injected syntheticresin in the cavity.

Since the discharging roller molded by the above die or manufactured bythe above method has enhanced flexural rigidity, even if force in theopposite direction to the discharging direction is applied onto thedischarging roller, the deformation of the discharging roller such as aflexure can be suppressed. Accordingly, the flip phenomenon of therecording medium due to the discharging roller can be prevented, andparticularly recording accuracy in recording on the whole surface can beimproved.

According to the invention, there is also provided a recording apparatuscomprising the above discharging roller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail preferred exemplary embodimentsthereof with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of the whole of the exterior structure ofan ink jet printer, in a state where a sheet ejection port is closed;

FIG. 2 is a perspective view of the ink jet printer, in a state wherethe sheet ejection port is opened;

FIG. 3 is a perspective view of the whole of the internal structure ofthe ink jet printer in a state where an upper housing is removed;

FIG. 4 is a sectional side view of an essential portion of the Ink jetprinter;

FIG. 5A is a perspective view showing a discharging roller in the inkjet printer;

FIG. 5B is a section view of the discharging roller;

FIG. 6 is a perspective view showing an upper die and a lower die usedin molding of the discharging roller, according to a first embodiment ofthe invention;

FIG. 7A is a plan view of the upper die and the lower die;

FIG. 7B is a section view taken along the line A-A in FIG. 7A;

FIGS. 8A and 8B are perspective views showing the lower die;

FIG. 9 is a side view showing a fitting part of the upper die and thelower die;

FIG. 10A is a plan view of the lower die, showing a fluid passage forcooling liquid;

FIG. 10B is a section view taken along the line B-B in FIG. 10A;

FIG. 11 is a section view of an injection molding machine incorporatingthe dies;

FIG. 12 is a section view showing a die used in molding of thedischarging roller with a gas injection method, according to a secondembodiment of the invention;

FIG. 13A is a perspective view showing a first related-art dischargingroller,

FIG. 13B is an enlarged perspective view of the first related-artdischarging roller, and

FIG. 14 is a section view showing a die used in molding of a secondrelated-art discharging roller with a gas injection method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will be described below in detailwith reference to accompanying drawings.

As shown in FIGS. 1 and 2, an ink jet printer 100 which is one ofrecording apparatuses comprises an upper housing 101 and a lower housing102. The upper housing 101 and the lower housing 102 are engaged witheach other by snap fitting.

On the rear side of the upper housing 101, a sheet feeding port 103 isformed. In this sheet feeding port 103, a sheet feeding tray 110 onwhich sheets to be supplied are stacked is attached. The sheet feedingtray 110 is attached so as to protrude to the diagonally upper backside,and holds the sheets in a slanting state. On the front side of the upperhousing 101, a sheet ejection port 104 is formed. On the front sides ofthe upper housing 101 and lower housing 102, a stacker 120 on which theejected sheets are stacked is provided.

The stacker 120 is attached to the front sides of the upper housing 101and lower housing 102 pivotably about a rotary shaft located at itslower portion. When the stacker 120 is not used, it is pivoted upward toclose the sheet ejection port 104. When it is used, it is pivoteddownward to open the sheet ejection port 104, and stops at a positionwhere it protrudes from the lower housing 102 to the diagonally upperfront side to receive the sheet in the slanting state. This stacker 120has two-stage structure comprising a first stacker member 121 and asecond stacker member 122 which is slidably attached to the firststacker member 121 at a distal end portion thereof. The second stackermember 122 is housed in the first stacker member 121 when it is notused, and pulled out from the first stacker member 121 when it is used.

A window 105 is formed from the upper portion of the upper housing 101to the front surface thereof. This window 105 is covered with atransparent or semitransparent openable cover 106. By opening this cover106, an exchanging work of ink cartridge and a maintenance work of theinternal mechanism can be readily performed. Further, a push button typeof power switch 131 and operational switches 132, 133 are provided onthe left backside of the upper housing 101.

As shown in FIG. 3, in the lower housing 102, a control board 130constituting a printer controller is placed vertically, and a recordingsection 140 constituting a print engine, a sheet feeder 150 and atransporter 160 shown in FIG. 4 are installed.

A control element and a memory element such as CPU, ROM, RAM, ASIC (theyare not shown), and other various circuit elements are mounted on thecontrol board 130. At the upper end of the control board 130, lightemitting diodes 133 and 134 are located protrusively, which emit lightsrespectively when the power switch 131 or the operational switches 132,133 are pushed on, whereby a user can confirm switch-ON.

The recording section 140 comprises a carriage 141, a recording head142, a carriage motor 143, a timing belt 144, and a suction pump 145. Ona sheet transported by the transporter 160, data is recorded by therecording head 142 mounted on the carriage 141 scanned by the carriagemotor 143 and the timing belt 144. From ink cartridges 146 of fourcolors, for example, yellow, magenta, cyan, and black, housed in thecarriage 141, each color ink is supplied to the recording head 142 sothat full color printing can be performed.

The feeder 150 comprises the sheet feeding tray 110, a sheet feedingguide 111, a sheet feeding roller 151, a hopper 152, and a separationpad 153. Sheets P stacked on the sheet feeding tray 110 and aligned bythe sheet feeding guide 111 are pushed against the sheet feeding roller151 with the separation pad 153 by rising of the hopper 152 withrotation of the sheet feeding roller 151, separated one by one from theuppermost sheet P, and transported to the transporter 160.

The transporter 160 comprises a feeding roller 161, a driven roller 162,a discharging roller 163, a serrated roller 164, a sheet feeding motor165, and the stacker 120. The sheet P supplied from the feeder 150 istransported to the recording section 140 while being held between thefeeding roller 161 driven by the sheet feeding motor 165 and the drivenroller 162, and further transported to the ejected sheet stacker 120while being held between the discharging roller 163 driven by the sheetfeeding motor 165 and the serrated roller 164.

As shown in FIGS. 5A and 5B, the discharging roller 163 is formed sothat a shaft portion 163 made of plastics elongates longer than at leastrecordable maximum sheet width and has a hollowed portion 163 cextending axially. Further, plural roller portions 163 b made ofelastomer such as rubber are joined to the shaft portion 163 a at aconstant interval. The shaft portion 163 a of the discharging roller 163is molded by an injection method or a gas Injection method whichgenerates a void that can prevent a sink and a warp by suppressinginternal stress produced when molding is performed using a die. Theroller portion 163 b of the discharging roller 163 is molded on theshaft portion 163 a by an injection method.

Since the shaft portion 163 a of the discharging roller 163 is thusformed in the hollowed shape having larger sectional area than sectionalarea of the relate-art discharging roller 1, flexural rigidity of thisdischarging roller 163 can be enhanced more than that of the related-artdischarging roller 1. Specifically, the diameter Dr1 (see FIG. 5B) is11.26 mm and the diameter Ds1 is 8.25 mm Therefore, the proportion ofthe outer diameter of the shaft portion to the outer diameter of theroller portion is 73.3%. Consequently, when the sheet is tensed betweenthe discharging roller 163 and the feeding roller 161, deformation ofthe discharging roller 163 such as a flexure can be suppressed.Therefore, a flip phenomenon caused by the discharging roller 163 can beavoided, and particularly recording accuracy in recording on a wholesurface can be improved.

As a material of the shaft portion 163 a of the discharging roller 163,thermoplastic resin is used, for example, ABS (copolymer ofacrylonitrile, butadiene and styrene), PS (polystrene), POM(polyacetal), modified PPE (polyphenylene ether), PC (polycarbonate),PBT (polybutylene terephthalate), and alloy system. Further, in order toheighten more the flexural rigidity, an additive such as GF (glassfiber), GB (glass beads), carbon, nylon, or potassium titanate is added.The amount of this additive is preferably 5 to 50% and particularly 10to 30% in order to further enhance the flexural rigidity.

As shown in FIG. 6, in a die 200 used in molding of the shaft portion163 a of the discharging roller 163, according to a first embodiment ofthe invention, cavity portions 201 and 202 are formed in order to moldone shaft portion 163 a of the discharging roller 163, and the die 200comprises an upper die 210 and a lower die 220 that are divided in theradial direction of the discharging roller 183. Here, since theconventional shaft portion of the discharging roller, formed of metal ishigh in rigidity, distortion can be prevented by double point supportstructure in which both ends are supported. However, since the shaftportion 163 a of the discharging roller 163 according to the inventionis formed of plastics that is lower in rigidity than the metal, fivepoint support structure in which not only the both ends but alsointermediate portions are supported is adopted to prevent thedistortion.

Since molding accuracy of each bore part in the shaft portion 163 a ofthe discharging roller 163 affects greatly accuracy of rotation of thedischarging roller 163, in order to improve the molding accuracy, theupper die 210 and the lower die 220 are respectively divided into threeparts at portions where a part other than the bore portions is molded.In other words, each bore section including at least one bore portion ismolded by a single die (a first upper die 211, a second upper die 212, athird upper die 213, a first lower die 221, a second lower die 222, anda third lower die 223) as shown in FIGS. 6, 7A and 7B.

Thus, through-work such as wire cut electrical discharge machining orcutting can be performed at the time of manufacturing the die, workingaccuracy of the die can be enhanced, and a die manufacturing cost can bereduced. Accordingly, the molding accuracy of the shaft portion 163 a ofthe discharging roller 163 can be improved, and the eccentric rotationof the discharging roller 163 can be suppressed. Further, since thesectional shape of the shaft portion 163 a of the discharging roller 163is simplified, a cost of the discharging roller 163 can be reduced.

Due to limitation of a shape in the vicinity of each bore portion, theremay be portions where the cavity portions 201 and 202 cannot becollectively formed However, insert dies 214 and 224 are inserted intothese portions to obtain desired shape of the cavity portions. FIGS. 8Aand 8B are perspective views showing the second lower die 222 in detail.In this second lower die 222, five insert dies 224 are inserted. Eachinsert die 224, is inserted into a through hole 222 a from a bottom face222 c side to constitute a part of the cavity portion 202. Though notshown, the first upper die 211, the second upper die 212, the thirdupper die 213, the first lower die 221, the third lower die 223 havealso the similar structure.

As shown in FIG. 9, a fitting part 215 of the upper die 210 and afitting part 225 of the lower die 220 are formed in the shapes ofconcave and convex that can be fitted to each other, and lower corners215 a of the upper fitting part 215 and the upper corners 225 a of thelower fitting part 225 are tapered so as to facilitate the fittingoperation.

Since the cavity portion 201 in the upper die 210 and the cavity portion202 in the lower die 220 can be faced with each other with highaccuracy, occurrence of flash extending in the axial direction of theperiphery of the shaft portion 163 a can be suppressed and the moldingaccuracy can be improved, so that the eccentric rotation of thedischarging roller 163 can be suppressed.

As shown in FIGS. 10A and 10B, the cavity portions 201 and 202 areheat-regulated. Inside of this second lower die 222, a fluid passage 204through which cooling liquid (e.g., water) for heat regulation of thecavity portion 202 flows is formed. As shown in FIG. 10B, the fluidpassage 204 extends perpendicularly from a bottom face 222 c at one endface 222 b side, it turns at a nearly right angle, extends from one endface 222 b side to the other end face 222 d side, and thereafter turnsat a nearly right angle to run through the bottom face 222 c at theother end face 222 side. Such the fluid passages 204, as shown in FIG.10A, are formed respectively on both widthwise sides of the cavityportion 202. Though not shown, the similar fluid passages are formed inthe first lower die 221 and the third lower die 223.

FIG. 11 is a section view showing a state where the die 200 is attachedto a die attaching portion 300 of an injection molding machine. In thedie attaching portion 300 of the injection molding machine, a fluidpassage 301 through which cooling liquid (e.g., water) forheat-regulating the die attaching portion 300 Itself flows is formed.Moreover, a fluid passage 302 through which cooling liquid forheat-regulating the cavity portions 201, 202 is formed so as tocommunicate to the fluid passage 204 of the die 200.

Hereby, since the inner surfaces of the cavity portions 201, 202 can becooled, when the melted plastic is injected, the outer surface ofplastic is solidified in a state where it is adhered onto the innersurfaces of the cavity portions 201, 202, and void is easy to beproduced on the inside thereof. Therefore, occurrence of internal stressof molded products for the shaft portion 163 a can be suppressed, sothat a sink and a warp can be prevented. Further, dimensional accuracyof outer diameter of the shaft portion 163 a can be improved, so thatthe eccentric rotation of the discharging roller 163 can be suppressed.Further, since the die 200 is cooled relatively quickly, an operationcycle for molding can be reduced.

Further, as the injection method, a gas injection method can be adopted.FIG. 12 shows this configuration as a second embodiment of theinvention. To a die attaching portion of an injection molding machine ofthis embodiment, a die 400 and a die 450 are attached. The die 400 hasthe similar structure as the die 200, in which cavity portions 401, 402for molding one shaft portion 163 a of a discharging roller 163 areformed. An auxiliary cavity 451 is attached to an exhaust port 404.

Under a condition that the cavity portions 401, 402 of the die 400 areheat regulated at a predetermined temperature, the predetermined amountof the melted plastic is injected from an injection port 403 of the die400. Subsequently, the predetermined amount of gas is injected from theinjection port of the die 400. Hereby, a plastic outer surface cominginto contact with the inner surfaces of the cavity portions 401, 402 isquickly cooled and pressed by gas pressure from the plastic inside.Therefore, the plastic is solidified in a state where it is adhered ontothe inner surfaces of the cavity portions 401, 402.

Melting plastic inside the plastic between the injection port 403 of thedie 400 and the exhaust port 404 is pushed out from the exhaust port 404by gas and fed out into the auxiliary cavity 451. Hereby, occurrence ofinternal stress of molded products for the shaft portion 163 a of thedischarging roller 163 can be suppressed, so that the sink and the warpcan be prevented. Further, the dimensional accuracy of outer diameter ofthe shaft portion 163 a can be improved, and a uniform hollowed portion163 c can be formed stably in the shaft portion 163 a throughout theentire region in the axial direction. Therefore, the eccentric rotationof the discharging roller 163 can be suppressed.

Though the invention has been described in the above variousembodiments, it is not limited the above embodiments but may be appliedalso to other embodiments within the scope of the appended claims. Forexample, though the ink jet printer has been described as an example ofa recording apparatus, the invention is not limited to this but can beapplied to another recording apparatus having a discharging roller, forexample, a thermal transfer type printer, and an ink jet type or thermaltransfer type facsimile or copying machine.

1-15. (canceled)
 16. A discharging roller which discharges a recordingmedium from a recording apparatus, comprising: a shaft portion,comprised of synthetic resin and formed with a hollow space; and aroller portion, formed on an outer periphery of the shaft portion,wherein a diameter of the hollow space is identical at a portion formedwith the roller portion and a portion formed without the roller portion.17. The discharging roller as set forth in claim 16, wherein thesynthetic resin is comprised of an additive to enhance stiffness of theshaft portion.
 18. The discharging roller as set forth in claim 16,wherein a proportion of an outer diameter of the shaft portion withrespect to an outer diameter of the roller portion is not less than60.5%.
 19. A recording apparatus, comprising the discharging roller setforth in claim 16.